1. Field of the Invention
The present invention relates to a switching circuit including a voltage-driven main switching element connected in series to a winding of a transformer which has primary and secondary windings being insulated from each other.
2. Description of the Related Art
FIG. 6 shows an example of a conventional switching circuit (switching regulator), and FIG. 7 is a graph showing the operating waveform of the switching circuit. In this switching circuit, a voltage-driven main switching element 102 is connected in series to a primary windings of a transformer 101, the primary and secondary windings thereof being insulated from each other. The output of a drive circuit 103 is connected to the control terminal of the main switching element 102, and the drive circuit 103 applies a frequency-controlled drive pulse to the main switching element 102.
However, in the structure described above, the switching speed is dependent on the rise of the drive signal, the rising speed, and the impedance of the drive circuit 103. Thus, in the case that the output impedance of the drive circuit 103 is high or in the case that the switching speed is slow, as shown in FIG. 7, there are the problems that the rise slows and the switching loss increases because the current passes through the active area of the main switching element 2.
In order to reduce the switching loss, it is necessary to increase the switching speed. However, there is the problem that this is limited by the performance of the drive circuit 103. In addition, in particular, because the speed of the drive is dependent on the speed of the control circuit and the like, it is necessary to select a control circuit with a good performance in order to increase the speed.
In consideration of the problems described above, it is an object of the present invention to provide a novel switching circuit that makes possible increasing the switching speed and decreasing the switching loss.